Light emitting diode (LED) is a highly efficient device to transform electric energy into light in comparison to conventional incandescent bulbs. The most important part of an LED is the semi-conductor chip located in the center of the bulb. The LED chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross the junction into the p region. When an electron moves sufficiently close to a positive charge in the p region, the two charges “re-combine”. Each time an electron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light.
LEDs have advantages of small size, low driving voltage, fast response, resistance to vibration and long service life. They do dozens of different jobs and are found in all kinds of devices. Among other things, they form the numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. Collected together, they can form images on a jumbo television screen or illuminate a traffic light.
Common LED lamps usually can be divided into two kinds of monochromatic light and polychromatic light. The polychromatic light LED lamp usually includes several lamps being able to provide different colored lights under individual controls so as to perform blends of light change.
As shown in FIG. 1, a side view of an LED lamp unit disclosed in U.S. Pat. No. 6,577,073, a lamp unit 1000 mainly includes LED lamps 100, a reflector 110 and a power supply 120. The reflector 110 reflects the light produced from the LED lamps 100. The power supply 120 supplies power to the lamps 100. A number of, typically 10 to 200, LED lamps 100 are arranged on the bottom of the reflector 110 to provide the required luminosity. As shown in FIG. 2, each LED lamp includes blue and red LEDs and a phosphor. The blue LED produces an emission at a wavelength falling within a blue wavelength range. The red LED produces an emission at a wavelength falling within a red wavelength range. The phosphor is photoexcited by the emission of the blue LED to exhibit a luminescence having an emission spectrum in an intermediate wavelength range between the blue and red wavelength ranges.
In each LED lamp 100, the blue and red LEDs and the phosphor are integrated together within a single envelope. The lamp unit 1000 is composed of a plurality of such LED lamps. In comparison with prior arts that individual LED of monochromatic light being used, the LED lamp 100 of the prior patent saves about half of the space and cost of package.
However, in FIG. 1, the whole assembly of the plurality of LED lamps 100 in envelopes still occupies much area and decreases the number of possible LED lamps in the cluster and the luminosity of the lamp unit 1000 in the limited space.
There is further a problem that when arranging the LED lamps 100 tightly to get higher luminosity, the heat generated from the LED lamps is hard to be dissipated. The reflector 110 thermally coupled through solid conduction to the LED lamps 100 is insufficient for dissipating the heat. The heat accumulation will influence the service life of the lamp unit 1000.